Field of the Invention
This invention relates to rotary regenerative air heaters for transferring waste heat from boiler flue gas to combustion air and, more particularly, to a new and improved linkage connected between the air heater's seal and duct hood frames.
In one type of rotary regenerative air heater, a cylindrical heat exchange mass and a containment structure, called the stator, is positioned stationary between the inlets and outlets of the air and gas ducts. The stator is a radially compartmented steel shell packed with a multiplicity of plates, arranged to provide an axial passage therethrough, such that the gas and air flow in an axial direction through the cylindrical heat exchange mass. The plates embody shapes, materials and thicknesses designed to provide optimum heat transfer, low pressure drop, resistance to corrosion, and ease of cleaning.
Air ducts at each axial end of the stator include air duct hoods, co-axially aligned with the cylindrical heat exchange mass, which are secured to a central drive shaft for co-axial rotation in relation to the cylindrical heat exchange mass. Each of the air duct hoods comprises a respective central flow inlet or outlet passage centrally mounted between, and in fluid communication with, two diametrically opposite hood segments or sectors for the passage of air to or from the heating mass. The hood segments of each of the air duct hoods are generally pie-shaped and circumferentially spaced from each other.
The gas ducts are arranged stationary, also at the opposite ends of the stator, and surround the rotating air duct hoods.
The air duct hoods, at opposite ends of the heat exchange mass, rotate synchronously so that alternate radial sectors of the mass of plates are alternately exposed to a hot flue gas stream and then cooled by a combustion air stream thereby effecting a regenerative heating and cooling cycle.
Sealing between the stationary and rotating components is achieved by articulated seal frames which are springmounted to the rotating air duct hoods. As the stator expands or contracts, the frames adapted to the stator's periphery in order to maintain an effective seal at various boiler loads. The seal frame, which extends along the peripheries of the hood segments adjacent the heat exchange mass, carries a sealing strip. The sealing strip is resiliently urged against cylindrical and radial end surfaces of the stator. During rotation of the air duct hood, the sealing strip slides along the end surfaces in sealing relationship with the stator.
An expansion joint is connected between the seal frame and the air duct hood to accommodate relative thermal displacement.
The seal frame and the air duct hood have been connected to each other by ball and socket drag linkages which transmit the driving torque and dead load forces between the air ducts and sealing frame as disclosed, for example, in U.S. Pat. Nos. 3,321,010 and 3,319,705. The linkage should allow coplanar axial movement of the ducts relative to the frame. Coplanar movement is critical to the maintenance of free rotary motion of the rotating surface relative to the stationary surface. Nonplanar movement due to thermal growth, for example, can result in seizure or intermittent binding of the rotating member. Such problems have been experienced in arrangements utilizing ball and socket drag link connections in respect of horizontal shaft regenerative air heaters having rotating duct connections and a stationary mass of steel plates for heat absorption.